A device that keeps extra-close tabs on the ups and downs of blood glucose levels reveals that most people see only a partial picture of the sugar circulating in their blood, according to a study by researchers at the Stanford University School of Medicine.

It turns out that the level of sugar in an individual’s blood—especially in individuals who are considered healthy—fluctuates more than traditional means of monitoring, like the one-and-done finger-prick method, would have us believe. Often, these fluctuations come in the form of “spikes,” or a rapid increase in the amount of sugar in the blood, after eating specific foods—most commonly, carbohydrates.

“There are lots of folks running around with their glucose levels spiking, and they don’t even know it,” said Michael Snyder, PhD, professor and chair of genetics at Stanford and senior author of the study. The covert spikes are a problem because high blood sugar levels, especially when prolonged, can contribute to cardiovascular disease risk and a person’s tendencies to develop insulin resistance, which is a common precursor to diabetes, he said.

“We saw that some folks who think they’re healthy actually are misregulating glucose—sometimes at the same severity of people with diabetes—and they have no idea,” Snyder said.

The insight came to him after he and collaborators at Stanford gave study participants a continuous glucose-monitoring device, which superficially pokes into the surface layer of the skin and takes constant readings of sugar concentrations in the blood as it circulates. With the constant readouts providing more detailed data, Snyder’s group saw not only that glucose dysregulation is more common than previously thought, but they also used the data to start building a machine-learning model to predict the specific foods to which people spike. The goal is to one day use the framework to compile data from an individual and, based on their continuous glucose readout, direct them away from particularly “spikey” foods.

The study was published online on July 24 in PLOS Biology. Graduate student Heather Hall, research dietician Dalia Perlman, and postdoctoral scholar Alessandra Brechi, PhD, share lead authorship.